If you would like to take advantage of such an option, you are also opting in to taking on an operational burden. That burden is exactly maintaining a set of backup keys and testing them on a regular basis.

And that's why "everyone should just use yubikeys" is never going to happen.

Everyone already pays the same operational burden with their house keys, which are far more difficult to manage for the average person (as they leave the house constantly). It's worked fine for hundreds of years.

If you lose your house keys, you get a lock smith to break into your house for you - your house doesn't become unusable forever more.

If you ever need to have this done, you'll realise how much house keys and door locks for many cases really only stop the opportunistic "pull the handle and see if it opens" attack. If your door has above average security they'll need to drill the lock, but the time I had to call one they could just push a tool through the letter box and break/move the bolt by applying leverage from the "indoor" side.

> If you lose your house keys, you get a lock smith to break into your house for you - your house doesn't become unusable forever more.

Same with 2FA. Just like a Locksmith it's a "human in the loop" situation where you'll need to give identification etc.

The rest of your post isn't relevant it's just about picking door locks.

House keys don't just randomly break the way electronics sometimes do, though.

I would bet that door locks and keys break pretty often. I know I've had many door locks that you had to wiggle just right.

I agree with this, it was my original expectation.